1. Field of the Invention
The present invention relates to a double feed detection method of recording media or documents, and a double feed detection apparatus.
More specifically, the present invention relates to a method for detecting double feed of sheet materials (feeding and conveying two or more sheets of recording media or documents) in a sheet feeding mechanism or a conveying mechanism used in a copier, a printer, a fax, an image reading scanner, or an automatic document feeder.
2. Related Background Art
FIG. 20 shows a configuration of a sheet feeding apparatus (a sheet material feeding apparatus) used in an image reading apparatus that can continuously read several sheets of overlapping documents (sheet materials) for fax or copy. In FIG. 20, reference numeral 9110 denotes a sheet feeding tray; 9101, a batch of documents; 9102, a sensor; 9103, a separation pad; 9105, a securing end; and 9106, a sheet roller.
The sensor 9102 detects that the documents 9101 are set on the sheet feeding tray 9110, and a detection signal is transmitted to a main unit. The separation pad 9103 provided above the sheet roller 9106 separates, one by one, leading ends of the documents 9101 placed in a slanting position on the sheet roller 9106 so as to facilitate sheet feeding.
The separation pad 9103 is pressed downward by a spring 9104, and an upper end of the spring 9104 is secured by the securing end 9105. Specifically, in the sheet feeding apparatus, the leading ends of the documents 9101 that abut against the separation pad 9103 are gradually displaced and separated one by one, due to the weight of the documents, and the separation pad 9103 being placed in the slanting position with respect to an inserting direction of the documents.
The set documents 9101 are fed one by one to a pair of conveying rollers 9107 by the sheet roller 9106. A document leading end detection sensor 9113 notifies the main unit that a leading end of a document reaches the conveying roller 9107. Then, the documents 9101 are successively conveyed. The above example relates to the sheet feeding apparatus used in the image reading apparatus, but a sheet feeding mechanism can be naturally applied to an image forming apparatus such as a copier or a printer.
However, in the above configuration, although the documents (or recording media) are resistant to double feed, whether the fed or conveyed documents are double fed or not cannot be determined (detected), and thus even if the documents are double fed, image reading (or image forming) is performed based on one sheet of document (or one sheet of recording medium) being conveyed. This prevents appropriate image reading or image forming.